1. Field of Invention
The present invention relates to an actuator, and particularly to an actuator for driving a release mechanism of a clutch.
2. Background Information
A device using an electric motor has been developed as a device for setting a clutch device of a vehicle to either a power transmitted (clutch-on) state or a power blocked (clutch-off) state. For example, a device described in Japanese Laid-open Patent Application No. JP-A-2003-194101 includes a motor, a motion conversion mechanism configured to convert a rotary motion of a motor into a linear motion, and a mechanism configured to drive a release mechanism of a clutch by means of the linear motion produced as a result of conversion by the motion conversion mechanism.
In general, the clutch device is configured to produce the clutch-on state by causing a diaphragm spring to press a clutch disc, while being configured to produce the clutch-off state by causing the release mechanism to release the pressing force of the diaphragm spring. Therefore, when the clutch-off state is produced by actuating the release mechanism in the device as described above, chances are that driving force is reversely applied from the release mechanism side due to the pressing force of the diaphragm spring. Where a motor is configured to be rotatable in response to such reverse driving from the release mechanism side, a member on the release mechanism side cannot be locked.
In view of the above, for the purpose of locking the release-mechanism side member, there are provided a method of constantly supplying electric power to the motor and a method of actuating a self-lock function in a path of transmitting power from the motor to the release mechanism. In Japanese Laid-open Patent Application No. JP-A-2003-194101, for instance, the motion conversion mechanism is composed of a worm gear and a worm wheel, and the self-locking function is configured to be actuated against reverse driving from the release mechanism side.